Chapter 1: Introduction
46
1 Chapter 1: Introduction Our goal: get “feel” and terminology more depth, detail later in course approach: use Internet as example Overview: what’s the Internet what’s a protocol? network edge network core access net, physical media Internet/ISP structure performance: loss, delay protocol layers, service models network modeling
description
Our goal: get “feel” and terminology more depth, detail later in course approach: use Internet as example. Overview: what’s the Internet what’s a protocol? network edge network core access net, physical media Internet/ISP structure performance: loss, delay - PowerPoint PPT Presentation
Transcript of Chapter 1: Introduction
1
Chapter 1: Introduction
Our goal: get “feel” and
terminology more depth, detail
later in course approach:
use Internet as example
Overview: what’s the Internet what’s a protocol? network edge network core access net, physical media Internet/ISP structure performance: loss, delay protocol layers, service models network modeling
2
What’s the Internet: “nuts and bolts” view
local ISP
companynetwork
regional ISP
router workstation
servermobile
protocols control sending, receiving of msgs e.g., TCP, IP, HTTP, FTP,
PPP
Internet: “network of networks” loosely hierarchical public Internet versus private
intranet
Internet standards RFC: Request for comments IETF: Internet Engineering
Task Force
3
Network Equipment
Ethernet Switches
Wiring Closet
Ethernet
4
Network Equipment
Wireless LAN base station
Cisco Routers
Cable Modem
5
What’s the Internet: a service view communication
infrastructure enables distributed applications: Web, email, games, e-
commerce, file sharing
communication services provided to apps: Connectionless unreliable connection-oriented reliable
6
What’s a protocol?
a human protocol and a computer network protocol:
Hi
Hi
Got thetime?
2:00
TCP connection req
TCP connectionresponseGet http://www.awl.com/kurose-ross
<file>time
7
A closer look at network structure:
network edge: applications and hosts
network core: routers network of networks
access networks, physical media: communication links
8
The network edge: end systems (hosts):
run application programs e.g. Web, email at “edge of network”
client/server model client host requests, receives
service from always-on server e.g. Web browser/server; email
client/server
peer-peer model: minimal (or no) use of dedicated
servers e.g. Gnutella, KaZaA
9
Network edge: connection-oriented service
Goal: data transfer between end systems
handshaking: setup (prepare for) data transfer ahead of time
TCP - Transmission Control Protocol
TCP service [RFC 793] reliable, in-order byte-
stream data transfer flow control congestion control
10
Network edge: connectionless service
Goal: data transfer between end systems
UDP - User Datagram Protocol [RFC 768]: connectionless unreliable data
transfer no flow control no congestion control
App’s using TCP: HTTP (Web), FTP (file
transfer), Telnet (remote login), SMTP (email)
App’s using UDP: streaming media,
teleconferencing, DNS, Internet telephony
11
The Network Core
mesh of interconnected routers
the fundamental question: how is data transferred through net? circuit switching:
dedicated circuit per call: telephone net
packet-switching: data sent thru net in discrete “chunks”
12
Network Core: Circuit Switching
End-end resources reserved for “call”
link bandwidth, switch capacity
dedicated resources: no sharing
circuit-like (guaranteed) performance
call setup required
13
Circuit Switching: FDM and TDM
FDM
frequency
time
TDM
frequency
time
4 users
Example:
14
Network Core: Packet Switching
each end-end data stream divided into packets
user A, B packets share network resources
each packet uses full link bandwidth
resources used as needed
resource contention: aggregate resource
demand can exceed amount available
congestion: packets queue, wait for link use
store and forward: packets move one hop at a time
Bandwidth division into “pieces”
Dedicated allocation
Resource reservation
15
Packet Switching: Statistical Multiplexing
A
B
C10 Mb/sEthernet
1.5 Mb/s
D E
statistical multiplexing
queue of packetswaiting for output
link
16
Packet switching: store-and-forward Great for bursty data
resource sharing simpler, no call setup
Excessive congestion: packet delay and loss
Takes L/R seconds to transmit (push out) packet of L bits on to link or R bps
Entire packet must arrive at router before it can be transmitted on next link: store and forward
R R RL
17
Packet-switched networks: forwarding
Goal: move packets through routers from source to destination
datagram network: destination address in packet determines next hop routes may change during session
virtual circuit network: each packet carries tag (virtual circuit ID), tag determines next
hop fixed path determined at call setup time, remains fixed thru call routers maintain per-call state
18
Network Taxonomy
Telecommunicationnetworks
Circuit-switchednetworks
FDM TDM
Packet-switchednetworks
Networkswith VCs
DatagramNetworks
19
Access networks and physical media
Q: How to connect end systems to edge router?
residential access nets institutional access
networks (school, company)
mobile access networks
20
Residential access: point to point access
Dialup via modem ADSL: asymmetric digital
subscriber line Cable Modem: Hybrid Fiber Coax
(HFC)
21
Cable Network Architecture: Overview
home
cable headend
cable distributionnetwork (simplified)
server(s)
Typically 500 to 5,000 homes
22
Company access: local area networks
company/univ local area network (LAN) connects end system to edge router
Ethernet: shared or dedicated link
connects end system and router
10 Mbs, 100Mbps, Gigabit Ethernet
LANs: chapter 5
23
Wireless access networks
shared wireless access network connects end system to router via base station aka “access point”
wireless LANs: 802.11b (WiFi): 11 Mbps
wider-area wireless access provided by telco operator 3G ~ 384 kbps WAP/GPRS in Europe
basestation
mobilehosts
router
24
Home networks
Typical home network components: ADSL or cable modem router/firewall/NAT Ethernet wireless access
point
wirelessaccess point
wirelesslaptops
router/firewall
cablemodem
to/fromcable
headend
Ethernet
25
Physical Media
Bit: propagates betweentransmitter/rcvr pairs
physical link: what lies between transmitter & receiver
guided media: signals propagate in solid
media: copper, fiber, coax
unguided media: signals propagate freely, e.g.,
radio
Twisted Pair (TP) two insulated copper
wires Category 3: traditional
phone wires, 10 Mbps Ethernet
Category 5: 100Mbps Ethernet
26
Physical Media: coax, fiber
Coaxial cable: two concentric copper
conductors bidirectional baseband:
single channel on cable legacy Ethernet
broadband: multiple channel on cable HFC
Fiber optic cable: glass fiber carrying light
pulses, each pulse a bit high-speed operation:
100 Mbps Ethernet high-speed point-to-point
transmission (e.g., 5 Gps)
low error rate: repeaters spaced far apart ; immune to electromagnetic noise
27
Physical media: radio
signal carried in electromagnetic spectrum
no physical “wire” bidirectional propagation environment
effects: reflection obstruction by objects interference
Radio link types: terrestrial microwave
e.g. up to 45 Mbps channels
LAN (e.g., Wifi) 2Mbps, 11Mbps
wide-area (e.g., cellular) e.g. 3G: hundreds of kbps
satellite up to 50Mbps channel (or multiple smaller
channels) 270 msec end-end delay geostationary versus low altitude
28
Internet structure: network of networks
roughly hierarchical at center: “tier-1” ISPs (e.g., UUNet, BBN/Genuity, Sprint,
AT&T), national/international coverage treat each other as equals
Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
Tier-1 providers interconnect (peer) privately
NAP
Tier-1 providers also interconnect at public network access points (NAPs)
29
Tier-1 ISP: e.g., Sprint
Sprint US backbone network
30
Internet structure: network of networks
“Tier-2” ISPs: smaller (often regional) ISPs Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs
Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
NAP
Tier-2 ISPTier-2 ISP
Tier-2 ISP Tier-2 ISP
Tier-2 ISP
Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet tier-2 ISP is customer oftier-1 provider
Tier-2 ISPs also peer privately with each other, interconnect at NAP
31
Internet structure: network of networks
“Tier-3” ISPs and local ISPs last hop (“access”) network (closest to end systems)
Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
NAP
Tier-2 ISPTier-2 ISP
Tier-2 ISP Tier-2 ISP
Tier-2 ISP
localISPlocal
ISPlocalISP
localISP
localISP Tier 3
ISP
localISP
localISP
localISP
Local and tier- 3 ISPs are customers ofhigher tier ISPsconnecting them to rest of Internet
32
Internet structure: network of networks
a packet passes through many networks!
Tier 1 ISP
Tier 1 ISP
Tier 1 ISP
NAP
Tier-2 ISPTier-2 ISP
Tier-2 ISP Tier-2 ISP
Tier-2 ISP
localISPlocal
ISPlocalISP
localISP
localISP Tier 3
ISP
localISP
localISP
localISP
33
How do loss and delay occur?
packets queue in router buffers packet arrival rate to link exceeds output link capacity packets queue, wait for turn
A
B
packet being transmitted (delay)
packets queueing (delay)
free (available) buffers: arriving packets dropped (loss) if no free buffers
34
Four sources of packet delay
1. nodal processing 2. queueing
A
B
propagation
transmission
nodalprocessing queueing
3. transmission delay 4. propagation delay
35
“Real” Internet delays and routes
What do “real” Internet delay & loss look like? Traceroute program: provides delay measurement
from source to router along end-end Internet path towards destination. For all i: sends three packets that will reach router i on path towards
destination router i will return packets to sender sender times interval between transmission and reply.
3 probes
3 probes
3 probes
36
“Real” Internet delays and routes
1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms4 jn1-at1-0-0-19.wor.vbns.net (204.147.132.129) 16 ms 11 ms 13 ms 5 jn1-so7-0-0-0.wae.vbns.net (204.147.136.136) 21 ms 18 ms 18 ms 6 abilene-vbns.abilene.ucaid.edu (198.32.11.9) 22 ms 18 ms 22 ms7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms9 de2-1.de1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms11 renater-gw.fr1.fr.geant.net (62.40.103.54) 112 ms 114 ms 112 ms12 nio-n2.cssi.renater.fr (193.51.206.13) 111 ms 114 ms 116 ms13 nice.cssi.renater.fr (195.220.98.102) 123 ms 125 ms 124 ms14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms15 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms 133 ms16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms17 * * *18 * * *19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms
traceroute: gaia.cs.umass.edu to www.eurecom.frThree delay measements from gaia.cs.umass.edu to cs-gw.cs.umass.edu
* means no reponse (probe lost, router not replying)
trans-oceaniclink
37
Protocol “Layers”
Networks are complex! many “pieces”:
hosts routers links of various
media applications protocols hardware, software
Question: Is there any hope of organizing structure of
network?
Or at least our discussion of networks?
38
Why layering?
Dealing with complex systems: explicit structure allows identification, relationship of
complex system’s pieces modularization eases maintenance, updating of
system layering considered harmful?
39
Internet protocol stack
application: supporting network applications
transport: host-host data transfer network: routing of datagrams from
source to destination link: data transfer between
neighboring network elements physical: bits “on the wire”
application
transport
network
link
physical
40
messagesegment
datagram
frame
sourceapplicatio
ntransportnetwork
linkphysical
HtHnHl M
HtHn M
Ht M
M
destination
application
transportnetwork
linkphysical
HtHnHl M
HtHn M
Ht M
M
networklink
physical
linkphysical
HtHnHl M
HtHn M
HtHnHl M
HtHn M
HtHnHl M HtHnHl M
router
switch
Encapsulation
41
Internet History: Starring
Vint Cerf
Robert Kahn
Leonard Kleinrock
Lawrence Roberts
“Where Wizards Stay Up Late: The Origins of the Internet ,”K. Hafner, M. Lyon, Simon & Schuster.
42
Internet History
1961: Kleinrock - queueing theory shows effectiveness of packet-switching
1964: Baran - packet-switching in military nets
1967: ARPAnet conceived by Advanced Research Projects Agency
1969: first ARPAnet node operational
1972: ARPAnet demonstrated
publicly NCP (Network Control
Protocol) first host-host protocol
first e-mail program ARPAnet has 15 nodes
1961-1972: Early packet-switching principles
43
Internet History
1970: ALOHAnet satellite network in Hawaii
1973: Metcalfe’s PhD thesis proposes Ethernet
1974: Cerf and Kahn - architecture for interconnecting networks
late70’s: proprietary architectures: DECnet, SNA, XNA
late 70’s: switching fixed length packets (ATM precursor)
1979: ARPAnet has 200 nodes
Cerf and Kahn’s internetworking principles: minimalism, autonomy -
no internal changes required to interconnect networks
best effort service model stateless routers decentralized control
define today’s Internet architecture
1972-1980: Internetworking, new and proprietary nets
44
Internet History
Early 1990’s: ARPAnet decommissioned
1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995)
early 1990s: Web hypertext [Bush 1945, Nelson
1960’s] HTML, HTTP: Berners-Lee 1994: Mosaic, later Netscape late 1990’s: commercialization
of the Web
Late 1990’s – 2000’s: more killer apps: instant
messaging, P2P file sharing network security to forefront est. 50 million host, 100
million+ users backbone links running at
Gbps
1990, 2000’s: commercialization, the Web, new apps
45
Internet Growth
46
Introduction: Summary
Internet overview what’s a protocol? network edge, core, access
network packet-switching versus
circuit-switching Internet/ISP structure performance: loss, delay layering and service models history
You now have: context, overview,
“feel” of networking more depth, detail
coming up!
